The impact of different concentrations of cadmium and arsenic in soil on the growth, some biochemical and physiological properties in lemon balm (Melissa officinalis L.)

Four concentrations of sodium arsenate (NaH2As4O.7H2O) were investigated on lemon balm plants, including As1 = 0, As2 = 10, As3 = 20, and As4 = 30 mg As kg⁻¹ in the soil. Additionally, four concentrations of cadmium sulfate (CdSO4) were tested: Cd1 = 0, Cd2 = 10, Cd3 = 20, and Cd4 = 30 mg Cd kg⁻¹ in the soil. Cd and As exposure led to a 50.7% decrease in the dry weight of the aerial parts. Increasing the concentrations of Cd and As in the soil resulted in reductions of 18.5% and 32.01% in root dry weight, respectively. Both metals significantly lowered the concentrations of chlorophyll 'a' (72.2%) and carotenoids (71.6%), while simultaneously increasing anthocyanin levels 77.6% in the leaf tissues. The presence of Cd and As induced considerable oxidative stress, reflected by a 49.4% increase in catalase (CAT) activity and a 49.6% increase in superoxide dismutase (SOD) activity in the leaves. Furthermore, the concentrations of mineral elements such as N, P, and K were diminished in the leaves due to Cd and As. In lemon balm, a greater quantity of As compared to Cd was translocated to the aerial parts, with As exerting a more substantial effect than Cd. The concentration of Cd in the roots varied from 2.7 to 53.3 µg g⁻¹ dry weight, while in the aerial parts, it was increased by 1.5 times. For As, the concentration in the roots was elevated by 17.9 times, and in the aerial parts, it was increased 15.1 times